does it track straight if you have the wheel turned slightly to the right and hold it there?

you should not need a wheel alignment if you put the steering wheel back correctly.

however, this is what could've happened (not saying it did, but it could have..) and i think this because you said you turned the wheel to straight ahead and the alignment arrow underneath it was pointed off a little:

the last time your car got aligned, they did not use a steering wheel lock. instead they just adjusted the steering ties underneath and accidently bumped it a little when they locked the nuts on one side and that twist the wheel a little off.. so your true dead-ahead makes the car turn a bit...